1. Field of the Invention
The present invention is directed to a resistance weld pin, and more particularly relates to a welding pin adapted to attach batts of thermal insulation to the interior surface of ducts.
2. The Prior Art
In order to improve the energy efficiency of air conditioning and heating installations employing metal duct work, batts or sheets of insulation ranging from one to two inches are typically secured to the interior surfaces thereof. Attachment is conventionally effected by adhesive alone or in conjunction with headed metallic pins extending through the insulation and bonded to the metal as by impact fastening or welding.
Suitable welding pins are disclosed in U.S. Pat. Nos. 3,624,340 of Nov. 30, 1971; 3,835,285 of Sept. 10, 1974; 3,858,024 of Dec. 31, 1974; 4,429,209 of Jan. 31, 1984; 4,482,795 of Nov. 13, 1984; and 4,614,855 of Sept. 30, 1986.
In each of the noted patents (all of which are owned and/or licensed to the holder of rights under the instant application), the welding pins are attached by passing an electrical current along the shank of the weld pin while the sharpened tip of the pin is pressed against the duct, which is connected to a ground electrode.
While the noted structures are effective to secure the insulation material in position, they are all subject to certain disadvantages in terms of function and economy.
Specifically, since the pin must function as a conductor, the current carrying capacity and, hence, the diameter of the pins must be sufficiently great to carry the high current needed to effect a weld. The necessity for providing thickened shanks to carry welding current, in addition to increasing the cost of the pins, also provides a significant thermal bridge between the interior and the exterior of the ducts, reducing the thermal efficiency of the insulation.
Also, since the welding current passes through the entire length of the pin, the external surfaces of the shank are raised to high temperatures during the welding procedure, with resultant possible damage to the insulating material surrounding the pin.